The first six dynasties are known to Egyptologists as the Old Empire. Kings of the Fourth dynasty, Khufu, Khafra, and Menkaura, built the great pyramids of Giza, the largest of which is still one of the wonders of the world. Its huge granite blocks are planed with mathematical exactitude, and, according to Professor Flinders Petrie, have been worked by means of tubular drills fitted with the points of emeralds or some equally hard stone. It was left for the nineteenth century to re-discover the instrument when the Mont Cenis tunnel was half completed. The copper for the bronze tools employed by the workmen was brought from the mines of Sinai, where the Egyptian kings had kept an armed garrison for many generations; the tin mixed with the copper must have come from India and the Malayan Peninsula, or else from Spain and Britain. While the Fifth and Sixth dynasties were reigning, exploring expeditions were sent into the lands of the Upper Nile. The two dynasties had sprung from the island of Elephantinê, opposite Assuan; it was, therefore, perhaps natural that they should take an interest in the country to the south. One expedition made its way into the land of Punt, to the north of Abyssinia, and brought back a Danga dwarf, whose tribal name still survives under the form of Dongo. Later expeditions explored the banks of the Nile as far south as the country of the Dwarfs, as well as the oases of Libya. The Old Empire was followed by a period of decline. Egypt was overrun by barbarians, its kings lost their power, and the whole land suffered decay. The pyramid tombs of the Old Empire were entered and despoiled; the bodies of the monarchs within them were torn to pieces, and the precious objects that had been buried with them were carried away. As the power of the kings diminished, that of the great landowners and nobles increased; a feudal aristocracy grew up, which divided Egypt between its members, and treated the royal authority with only nominal respect. Memphis ceased to be the capital, and a new dynasty, the Ninth, was founded by the feudal prince of Herakleopolis, now Ahnas, south of the Fayyûm. For a time the Tenth dynasty succeeded in reducing its rebellious vassals to obedience, but the princes of Thebes steadily grew in strength, and at length one of them seized the throne of the Pharaohs and established the Eleventh dynasty. Thebes became the capital of the kingdom, and under the Twelfth dynasty was the capital of an empire.